1. Field of the Invention
This invention relates to combustion devices for hot air appliances, and more particularly, to a novel and improved combustion device for use with pressurized and zero-pressure hot air appliances. The invention is specifically concerned with a propane-air combustion device of the open-cycle external combustion, continuous-process type, which may be described as a fuel pressure driven nozzle mixer-diffuser-screen burner combustion device which generates a stream of heated air for the transfer of thermal energy to a load.
2. Description of the Prior Art
It is well known in the combustion device art to provide burners for hot air appliances. A disadvantage of such prior art combustion device is that they provide a fuel rich flame, and they are unable to entrain a sufficient amount of air to provide complete combustion and a clear air flame, as well as a low temperature flame. Examples of such prior art combustion devices for balloons are illustrated in U.S. Pat. Nos. 4,008,041 and 4,076,188. Other pertinent references are shown in U.S. Pat. Nos. 3,420,473, 3,833,338, 3,840,321 and 4,018,406. A further prior art reference is an article appearing in the "J. Aircraft" magazine, Vol. 15, No. 12, December 1978, which is entitled "Prediction of Performance of Low-Pressure-Ratio Thrust-Augmenter Ejectors", by J. A. C. Kentfield, University of Calgary, Alberta, Canada. Another prior art reference is an article by M. R. Seiler and E. F. Schum (Rockwell International, Columbus, Ohio) entitled "An Analytical and Experimental Investigation of Diffusers for VSTOL Thrust Augmenting Ejectors" which was presented at the AIAA Aircraft Systems and Technology Conference, Los Angeles, Calif., on Aug. 21-23, 1978. A copy of this article may be obtained from the American Institute of Aeronautics and Astronautics, 1290 Avenue of the Americas, New York, N.Y. 10019.
Still another prior art reference is an article by P. M. Bevilaqua and A. D. DeJoode of Rockwell International, Columbus Aircraft Division, Columbus, Ohio 43216, entitled "Viscid/Inviscid Interaction Analysis of Thrust Augmenting Ejectors", dated Feb. 28, 1978.
The inlet nozzle-diffuser structures in the last three mentioned articles are presented as having an optimum configuration thrust augmentation. However, a disadvantage of such inlet nozzle-diffuser structures is that they do not produce the highest entrainment ratio. The low velocity air-fuel mixture exiting the center section of the flame retention screen allows the screen to reach a high temperature and further slow the air-fuel mixture flow at center. The result is to greatly impede the inlet nozzle-diffuser performance.